This proposal contains plans for studies on several different topics in transfer RNA research: (1) genetic and biochemical studies on the regulation of the biosynthesis of tRNA and aminoacyl-tRNA synthetases; (2) comparative studies on the structure of specific tRNA precursors from E. coli, yeast and mammalian cells; (3) the preparation and use of tRNAs with photoreactive groups; (4) biochemical analysis of nonsense suppressor tRNAs in yeast. BIBLIOGRAPHIC REFERENCES: Studies on the Complex Between Transfer RNAs with Complementary Anticodons: I. Origins of Enhanced Affinity Between Complementary Triplets. H. Grosjean, D. Soll, and D.M. Crothers. J. Mol. Biol. 103, 499 (1976). The Isolation of Specific tRNA Precursors. T.S. Stewart, T. McCutchan, G. Vogeli, H. Grosjean and D. Soll. In Synthesis, Structure and Chemistry of Transfer Ribonucleic Acids and Their Components, Universytet im. Adama Mickiewicza, Poznan, 1976, in the press.